fixup! Make ROUTERLIST_PRUNING_INTERVAL 1 hr.

changes/bug27929

   o Minor bugfixes (periodic events):
     - Refrain from calling routerlist_remove_old_routers() from
       check_descriptor_callback(). Instead, create a new periodic
-      event that will run every minute even if Tor is not configured
+      event that will run once every hour even if Tor is not configured
       as onion router. Fixes bug 27929; bugfix on 0.2.8.1-alpha.